$all operator for matching all elements in MongoDB - Step-by-Step Execution

Concept Flow - $all operator for matching all elements

Start Query

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Check $all Operator

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For each element in $all array

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Does document array contain element?

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Reject Document

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All elements matched?

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Include

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Return matched documents

The $all operator checks if a document's array contains all specified elements. It tests each element and only returns documents matching all.

Execution Sample

MongoDB

db.products.find({ tags: { $all: ["red", "round"] } })

Finds products whose tags array contains both "red" and "round".

Execution Table

Step	Document tags	Check element 'red'	Check element 'round'	Result
1	["red", "round", "small"]	Yes	Yes	Include document
2	["red", "square"]	Yes	No	Reject document
3	["blue", "round"]	No	Yes	Reject document
4	["red", "round"]	Yes	Yes	Include document
5	["round"]	No	Yes	Reject document
Exit	-	-	-	All documents checked

💡 All documents checked; only those with both 'red' and 'round' included.

Variable Tracker

Variable	Start	Doc 1	Doc 2	Doc 3	Doc 4	Doc 5	Final
tags	-	["red", "round", "small"]	["red", "square"]	["blue", "round"]	["red", "round"]	["round"]	-
matches 'red'	-	true	true	false	true	false	-
matches 'round'	-	true	false	true	true	true	-
include document	-	true	false	false	true	false	-

Key Moments - 3 Insights

Why does a document with tags ["red", "square"] get rejected?

Because it does not contain the element 'round' required by $all, as shown in execution_table row 2 where 'Check element round' is No.

Does $all require the array elements to be in order?

No, $all only checks presence of all elements regardless of order, as seen in document 1 with tags ["red", "round", "small"] included despite order.

What happens if the document array is missing one element from $all?

The document is rejected, like document 5 missing 'red' and rejected in execution_table row 5.

Visual Quiz - 3 Questions

Look at the execution table, does the document with tags ["blue", "round"] match the query?

A Yes, because it has 'round'

B No, because it lacks 'red'

C Yes, because it has at least one element

D No, because it has 'blue'

💡 Hint

Check row 3 in the execution_table where 'matches red' is false and document is rejected.

At which step does the condition for including a document become false?

A When any element in $all is missing from the document array

B When the document array is empty

C When the document has extra elements

D When the document array has duplicates

💡 Hint

See execution_table rows 2, 3, and 5 where missing elements cause rejection.

If the query changes to $all: ["round"], which documents would be included?

A Documents with 'red' only

B Only documents with 'red' and 'round'

C Documents with 'round' regardless of 'red'

D All documents

💡 Hint

Focus on the $all array elements and their presence in document arrays.

Concept Snapshot

$all operator syntax:
{ field: { $all: [value1, value2, ...] } }
Returns documents where field array contains all listed values.
Order does not matter.
Useful to match multiple required elements in arrays.

Full Transcript

The $all operator in MongoDB is used to find documents where an array field contains all specified elements. The query checks each element in the $all array against the document's array field. If any element is missing, the document is excluded. Documents that contain all elements are included in the results. This operator does not require elements to be in order, only that all are present. For example, a query with $all: ["red", "round"] returns documents whose tags array includes both 'red' and 'round'. The execution table shows step-by-step checks for each document, confirming which elements are present and whether the document matches. This helps beginners understand how $all works by visualizing the matching process.